The use of bone stabilization/fixation devices to align or position bones is well established. Furthermore, the use of spinal bone stabilization/fixation devices to align or position specific vertebrae or a region of the spine is well established. Typically such devices use a coupling assembly to connect or link two or more surgical screws and/or pedicle screws together to stabilize the bone and/or joint around which the screws are fixed. The coupling assembly typically is comprised of a relatively rigid member such as a plate or a rod that is used to couple or join adjacent structures or parts of the anatomy. Once the coupled structures are spatially fixed in position, procedures can be completed, healing can proceed, and the like.
Conventional surgical and/or pedicle screw coupling systems, however, have several drawbacks. Those coupling systems are rather large and bulky, which can result in more tissue damage in and around the surgical site, both from when the coupling system is installed during surgery and from implant induced, post-operative tissue irritation and erosion. The relative bulk of the prior art devices may be particularly relevant in supra-fascial applications. The prior art coupling systems have a rod-receiving device that is delivered to the surgeon already coupled or attached to the head of the surgical screw, which poses two challenges: 1) this prevents certain surgical maneuvers (e.g. placing the screws prior to interbody work); and, 2) increases the carrying cost of the inventory. Furthermore, traditional coupling systems do not allow for varying the rod stiffness along a multi-segmented construct; certain indications may require a stiff rod over one segment and a flexible rod over another. Further, with traditional systems there is an inability to easily extend a fusion; that is to say that in a revision procedure the existing rod would need to be removed rather than just adding a short rod segment to the end of the coupling system. In addition, some of the prior art coupling systems include locking components (e.g., set screws and the like) that must all be carefully assembled together during the surgical procedure. Further, many traditional surgical screw system designs preclude the ability to be placed percutaneously over a guide wire, which makes these systems more difficult to install and maneuver during surgical procedures, including minimally invasive procedures.
Moreover, prior art devices require that the rod be assembled to the coupling device after the screw is inserted in the bone, which can be disadvantageous at times, whereas the option to assemble the rod to the coupling device outside the wound may prove valuable. Also, existing coupling systems necessitate simultaneous locking of all components, which prevents the ability to properly compress a coupling system along the rod because the angle relative to the surgical screw would change. Yet further still, to accommodate various anatomies and/or misplacement of surgical screws due to simple tolerance variances and/or error, requires a surgeon to bend the rod, thus further increasing cost and complexity. An example of such a prior art surgical screw system is disclosed in U.S. Pat. Publ. No. 2008/0140075, titled Press-On Pedicle Screw System, which has a common inventor with this application and is owned by the assignee of this application.
Thus, there exists a need for a coupling system for surgical screws that accommodates and allows for misalignment and/or varying tolerances and/or differing anatomies and/or geometries.
There also exists a need for a coupling system or assembly that is smaller in profile than existing coupling systems, which may be particularly applicable to supra-fascial placement.
There is a need for coupling systems better adapted for use over a guide wire, and with minimally invasive surgical techniques, such as endoscopy.
There also exists a need for a coupling system that comprises fewer components (e.g., no set screws), has a lower profile, and accommodates easier assembly and/or disassembly in-situ (i.e., within the patient) and before implantation than existing coupling systems. This includes the ability to assemble the rod to the coupling/connecting device prior to placement in the surgical wound.
There also exists a need for a coupling system that allows for varying the stiffness of the coupling system. For example, it may be appropriate to apply a rigid rod to a fused segment and a flexible member to an adjacent segment.
There is a need for a system that provides for simple extension of a coupling system in revision surgery.
There is a need to decrease the carrying cost of inventory by eliminating the requirement of placing a connecting-device on each pedicle screw prior to implantation.
There is a need to eliminate rod bending in multi-segment constructs.